Since the drought began in fall 2010, Medina Lake has dropped steadily and is less than 6 percent full, according to the Texas Water Development Board.

On Monday, SAWS plans to announce it will replace the Medina supply for the South Side with water from the Edwards Aquifer.

This isn't the first time the utility has closed the plant, which it acquired when it merged with the Bexar Metropolitian Water District. Last summer, the plant was mothballed for three months because of similar concerns over increases in algae growth and carbon compounds in the water.

This time the drought has made it impossible to make firm plans about a restart date for the plant.

SAWS spokeswoman Anne Hayden said the utility will wait for the lake to start refilling before the plant is put back in operation.

“We will only know once Medina Lake gets significant rain,” she said. “It could be August or September.”

Medina Lake hasn't been full since 2008. It usually doesn't fill unless there is a single huge rainstorm or several months of above-average rainfall, according to TWDB records.

The Climate Prediction Center is forecasting above-average temperatures through December for South Texas, but is giving equal chances to above-average or below-average rainfall.

For the last six months, Medina Lake has lost between 90 and 100 acre-feet of water a day, the TWDB said. If that rate continues, there will not be any water to release from the lake in less than five months.

Before it shut its plant, SAWS was ordering 14 acre-feet a day from the BMA district.

The rest went to seepage around the dam, percolation into the ground and evaporation.